Radio frequency shield for nuclear magnetic resonance procedures

ABSTRACT

An apparatus and method for providing RF shielding for performing nuclear magnetic resonance (“NMR”) procedures, comprising a radio-opaque holder in combination with radio-opaque magnet components to form an RF shield around a patient undergoing an NMR procedure. In embodiments, a radio-opaque holder having a radio-opaque bottom portion and a radio-opaque canopy is adjoined to an NMR magnet having a radio-opaque cryostat and a radio-opaque service end cap to form an RF shield. A patient is placed on a patient support unit located in the holder bottom portion. The patient support unit, including the patient, is then inserted into the cavity of the NMR magnet and a canopy is placed on top of the bottom portion of the holder. An RF shield is thus created comprising the canopy, the bottom portion, the cryostat of the magnet, and an end cap on the service end of the magnet.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to nuclear magnetic resonance(“NMR”) procedures, such as magnetic resonance imaging (“MRI”), magneticresonance angiography (“MRA”) and magnetic resonance spectroscopy(“MRS”). More specifically, the present invention relates to a system,method and apparatus for shielding against unwanted radio frequencysignals when performing an NMR procedure. The invention is designed forclinical veterinary applications, but could be employed for any NMRapplication.

[0003] 1. Related Art

[0004] NMR technology has provided physicians with the ability to viewthe inside of a human patient's body in order to form accurate diagnosesand prescribe proper treatments. Because NMR procedures rely on thedetection of RF signals with low signal-to-noise ratios, NMR proceduresare typically conducted in environments that are substantially free ofunwanted RF signals. The usual manner by which a “clean” environment(that is, an environment substantially free of unwanted RF noise) isachieved is by shielding the room in which the NMR procedure takesplace. This approach involves building a contiguous radio-opaque screen,known as a faraday cage, to encompass an entire room—including floors,ceilings, and walls. All openings into the room, such as windows, doors,and penetrations for power supply and other cables, are formed in amanner that does not impair the integrity of the RF shield.

[0005] Doctors who practice veterinary medicine can benefit from thediagnostic capabilities of NMR technology. However, due to the costassociated with obtaining NMR equipment and providing a dedicated,RF-shielded room for the procedure, veterinarians typically are unableto offer NMR procedures to their patients. Accordingly, NMR proceduresare not readily available to most non-human patients; indeed, pet ownerswishing to have NMR procedures conducted on their pets normally have topay to have their pets taken after business hours to hospitals oroffices having NMR equipment for use with humans.

[0006] Thus, there is a need for a cost-effective way to provide doctorswho practice veterinary medicine with the ability to offer NMRprocedures to their patients.

SUMMARY OF THE INVENTION

[0007] Features and Advantages

[0008] The following features characterize some, but not necessarilyall, embodiments of the present invention.

[0009] One feature of an embodiment of the present invention is that itreduces the cost of NMR procedures by eliminating the need for adedicated, RF-shielded room for performing such procedures. By formingthe RF shield around the patient and RF coils, as opposed to around theNMR room itself, embodiments of the present invention facilitate the useinside the NMR room of electronic equipment to support NMR procedures aswell as of AC (rather than DC) lighting fixtures.

[0010] Another feature of an embodiment of the present invention is thatit enables the patient space to be climactically controlled, thusfacilitating the maintenance of the patient's temperature.

[0011] Another feature of an embodiment of the present invention is thatit provides an improved support unit for holding a non-human patientduring an NMR procedure.

[0012] Another feature of an embodiment a support unit of the presentinvention is that it provides the ability to modify an RF coilconfiguration for an anesthetized patient to image different parts ofthe patient's body without moving the patient.

[0013] Further features and advantages will become apparent followingreview of the detailed description set forth below or in the course ofpracticing the invention.

[0014] Summary

[0015] In summary, the invention comprises a radio-opaque holder forholding a patient support unit supporting a patient about to undergo anNMR procedure, and for providing, in conjunction with shielding providedby an NMR magnet, RF shielding for the procedure. In an embodiment, thepatient support unit can be moved from the holder into the magnet whenthe holder adjoins the magnet. In embodiments, the holder may comprise acanopy and a bottom portion such that when the canopy is placed over thebottom portion, a radio-opaque enclosure—which may be substantiallycylindrical in shape—is formed around the patient support unit. In anembodiment, the patient end of the holder is enclosed with radio-opaquematerial, for example as a result of the placement of the canopy on topof the bottom portion of the holder, or as a result of use of a separatepatient end cap. In an embodiment, the magnet end of the holder is open,and is configured so that, when the holder is adjoined with the openingof the NMR magnet, the RF shielding associated with the magnet(“magnet-RF-shielding”) and RF shielding associated with the holder(“holder-RF-shielding”) combine to form a continuous RF shield.

[0016] The holder may be formed to operate with existing NMR magnets, orspecialized NMR magnets may be produced to operate together with theholder as a system. For a magnet whose construction provides sufficientRF shielding (as, for example, a superconducting magnet whose innerdiameter comprises a cryostat made of radio-opaque material), the shieldmay be completed by the RF shield provided by the magnet itself combinedwith a radio-opaque service end cap that covers the service end of themagnet. In such embodiments, the result is a cylindrical RF shield fullyencompassing the patient, which has a length of approximately the lengthof the cavity of the magnet, plus the length of the holder.

[0017] The holder may comprise a base unit, which may enable the holderto be moved (for instance, by means of wheels or rollers) to adjoin themagnet in a manner that aligns the bottom portion of the holder with thebore of the magnet to facilitate insertion of the patient into themagnet cavity. The holder may be attachable to the magnet by means of adocking mechanism, for example.

[0018] In embodiments, the bottom portion of the holder is designed toinclude within it a patient support unit, typically on a longitudinaltrack formed on the bottom portion of the holder that can be alignedwith a similar horizontal track in the bore of the magnet. The alignmentof the tracks facilitates movement of the patient support unit from theholder into the magnet for an NMR procedure.

[0019] The patient support unit may be made of a material that slideswell on the bottom portion of the holder as well as in the bore of themagnet. A suitable combination of materials is, for example,Teflon-coated fiberglass for the patient support unit, and Teflon-coatedcarbon fiber for the bottom portion of the holder and the bore of themagnet (which may be a cryostat). In embodiments, the patient supportunit includes a bed that is configured to hold an animal, preferably inan inverted position. The bed may be formed substantially to match thecurvature of the animal's spine, and different-sized anddifferent-shaped beds (in some embodiments, on different patient supportunits) may be used to accommodate different sizes and shapes of animals.The patient support unit may include RF transmitter antennas andreceiver antennas, such as RF coils, that provide RF energy used in theNMR procedure. In embodiments, the bed includes lower RF coils as wellas connectors for upper RF coils for use forming, in conjunction withthe lower RF coils, volume coils for imaging parts of the patient's bodysuch as the head and abdomen. In embodiments, the RF coils are movablewith respect to the bed, to facilitate imaging different parts of thepatient's body.

[0020] The patient support unit of the invention may be used inconjunction with the holder of the invention, in which case theholder-RF-shielding and the magnet-RF-shielding provide RF shielding forthe NMR procedure. The patient support unit of the invention can also beused with holders that do not comprise RF shielding, or with NMR magnetsthat do not comprise RF shielding, as, for example, in cases where afaraday cage provides RF shielding for the NMR room.

[0021] The invention also includes a method for performing an NMRprocedure using the apparatus and system described above and in thisspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 depicts an embodiment of a holder of the invention,including a canopy, as it relates to an NMR magnet during an NMRprocedure.

[0023]FIG. 1A provides an illustration of a service end cap attached tothe service end of an NMR magnet.

[0024]FIG. 1B depicts an embodiment of a holder of the invention, withthe canopy removed, as it relates to an NMR magnet during an NMRprocedure.

[0025]FIG. 1C depicts an embodiment of a holder of the invention holdinga patient support unit of the invention.

[0026]FIG. 2 depicts the components that make up a patient support unitof an embodiment of the invention.

[0027]FIG. 2A depicts an embodiment of a patient support unit of theinvention.

[0028]FIG. 2B depicts an embodiment of a patient support unit viewedfrom the patient end.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] Definitions

[0030] As used in this specification, the following terms have thefollowing associated meanings.

[0031] “NMR procedure” refers to any procedure that relies on nuclearmagnetic resonance. Examples include, but are not limited to, magneticresonance imaging (“MRI”), magnetic resonance angiography (“MRA”), andmagnetic resonance spectroscopy (“MRS”).

[0032] “Radio-opaque” refers to a property of a material that enables itto block RF energy. A material described in this patent application as“radio-opaque” need not block all RF energy; it merely must block RFenergy to an extent that those with skill in the art would recognize itas providing sufficient RF shielding to prevent unwanted RF signals frominterfering with an NMR procedure. Radio-opacity depends on a number offactors, including the type of the material, as well as the thicknessand density of the component that uses the material, as well as thesensitivity and functioning of the equipment used to conduct the NMRprocedure. Examples of materials that are radio-opaque in the frequencyranges typically used for NMR procedures are metals such as copper,aluminum, stainless steel, beryllium, and titanium. A semi-transparentradio-opaque shield may be formed of a radio-opaque metal screen, suchas a copper screen, encased in acrylic.

[0033] “Non-ferromagnetic” refers to a material that is substantiallycomprised of materials other than ferromagnetic materials (materialswhich may be attracted to a magnet). Ferromagnetic materials aregenerally not used in the NMR environment because they will be attractedto the NMR magnet.

[0034] “Holder” refers to a member that supports, and (in someembodiments) surrounds, a patient support unit, and in embodiments ofthe invention may comprise a bottom portion, a canopy, a patient endcap, and a base, as described in more detail below with reference toFIGS. 1, 1A, 1B and 1C.

[0035] “Magnet end” (of a holder) refers to the end of the holder thatis adjoined to the magnet in an NMR procedure.

[0036] “Patient end” (of a holder) refers to the opposite end of theholder from the “magnet end.”

[0037] “Patient end” (of a magnet) refers to the end of the magnetcavity into which the patient is inserted.

[0038] “Service end” (of a magnet) refers to the opposite end of themagnet cavity from the patient end.

[0039] “Magnet-RF-shielding” refers to RF shielding associated with theNMR magnet, which may include RF shielding provided by the magnetcryostat and/or RF shielding provided by a radio-opaque service end capplaced over the service end of the magnet.

[0040] “Holder-RF-shielding” refers to RF shielding associated with theholder of the invention, which may include shielding provided by thebottom portion of the holder, the canopy, and/or a patient end cap.

[0041] “Animal” refers to nonhuman animals. While the embodiments of theinvention described in this specification relate to providing NMRprocedures for non-human animals, the present invention can also be usedfor providing NMR procedures to humans.

[0042] Detailed Description

[0043] An exemplary embodiment of the present invention will now bedescribed. Referring to FIGS. 1, 1A and 1B, a system for use in an NMRprocedure comprises a holder 103 (comprising bottom portion 105 andcanopy 109) and a magnet 115 and associated components (includingcryostat 117 and service end cap 119). Bottom portion 105, canopy 109,cryostat 117 and service end cap 119 are all radio-opaque. When theholder 103 is adjoined to the magnet 115 and service end cap 119 is putin place at the service end 118 of magnet 115, a substantially completeRF shield is formed, consisting of canopy 109, bottom portion 105,cryostat 117, and service end cap 119. The term “adjoined to,” as usedin this specification, refers to the position of holder 103 in relationto magnet 115 such that an RF shield is formed from holder-RF-shieldingand magnet-RF-shielding.

[0044] In the embodiment depicted in FIGS. 1 and 1B, bottom portion 105contains or is made of a non-ferromagnetic radio-opaque material. Asdepicted in FIG. 1B, bottom portion 105 includes longitudinal track 112for engaging a patient support unit, as depicted in FIGS. 2A and 2B. Asshown in FIG. 1B, when bottom portion 105 is adjoined to magnet 115,track 112 of bottom portion 105 aligns with track 121 of magnet 115, tofacilitate smooth transfer of the patient support unit from bottomportion 105 to magnet cavity 116. Bottom portion 105 may be attached toor integral with base 107, which may be mounted on wheels or casters formoving holder 103 to and from magnet 115.

[0045] In an embodiment, canopy 109 (depicted in FIGS. 1, 1B and 1C) isconstructed of or contains a radio-opaque material such as copper oraluminum. In an embodiment, canopy 109 is semi-transparent to facilitateobserving the patient during preparation and during an NMR procedure. Asuitable, radio-opaque semi-transparent canopy 109 can be fabricated byencasing a radio-opaque metallic screen, such as a copper screen, inacrylic. Canopy 109 can be a separate component of the holder 103, whichcan be placed on top of bottom portion 105 to form a cylindrical shield.In an embodiment, canopy 109 can be placed on bottom portion 105 withoutlocking canopy 109 into position. In some embodiments, the edges ofcanopy 109 comprise electrically conductive screen or other electricallyconductive connections so that a pressure applied to the bottom surfaceof the canopy 109 and the corresponding top surface of bottom portion105 will produce an electrical contact, thereby completing an RF shieldcomposed of bottom portion 105 and canopy 109. In some embodiments,clamps (not depicted) attached to bottom portion 105 swing upward toengage canopy 109, thereby providing the pressure useful in maintainingelectrical contact.

[0046] In alternative embodiments (not depicted), the canopy can behinged to either the magnet or the bottom portion of the holder. In oneexample of such an embodiment, the canopy comprises two halves, hingedto opposite sides of the bottom portion of the holder, such thatswinging the halves upward results in formation of the canopy. In suchembodiments, the holder may have a base in the shape of an inverted T,similar to that of base 107 depicted in FIGS. 1B and 1C, to accommodatethe canopy halves when the canopy is not in use. In embodiments wherethe canopy is hinged to either the magnet or the holder, the hinges andassociated components can also provide electrical contact useful incompleting the RF shield.

[0047] In the embodiments depicted in FIGS. 1, 1B, and 1C, canopy 109 isshaped so that when canopy 109 and bottom portion 105 are attached, theyform a cylinder that is closed at the patient end and open at the magnetend. The shape of the canopy is not critical to the invention; it merelymust provide room for patient support unit (such as patient support unit131 depicted in FIG. 1C), including the patient and any RF coils.

[0048] In other embodiments (not depicted), the RF shield formed by acanopy and a bottom portion is a cylinder that is open at both ends. Insuch embodiments, the patient end of the cylinder may be covered with apatient end cap to complete the RF shield. Such a patient end cap may bemade of radio-opaque metal, or of a radio-opaque metallic screen, suchas a copper screen, encased in acrylic, or other radio-opaque materials.In such embodiments, the RF and physiological connections to the patientend cap may be routed through apertures in the patient end cap. Thepatient end cap can be attached to the canopy or the bottom portion, orboth, by means of hooks, clasps, clamps, clips, screws, bolts, hinges,and other similar means.

[0049] The holder 103 of this invention can be designed to operate withexisting NMR magnets, or the holder 103 and magnet 115 can be designedand built as a system. In the embodiment depicted in FIG. 1, magnet 115is cylindrical in shape, and has a cylindrical magnet cavity 116extending through the length of magnet 115. Magnet 115 may be asuperconducting magnet, an electromagnet, or a permanent magnet.

[0050] In the case of a superconducting magnet, as depicted in FIG. 1B,the magnet 115 may have a cylindrical cryostat 117 formed on its innerdiameter. Cryostat 117 typically holds a cryogen, such as liquid helium,in which the superconducting magnet wire is contained. In embodiments ofthe present invention, cryostat 117 is made of radio-opaque material andprovides sufficient RF shielding to be used as a portion of the RFshield of the present invention. Because cryostats made of radio-opaquestainless steel are features of many existing NMR magnets, it may not benecessary to modify such magnets in order for them to operate with theholder of the present invention.

[0051] A holder 103 according to the present invention can also be usedwith an NMR magnet 115 that has a cryostat 117 that is not made ofradio-opaque material, or an NMR magnet, such as a permanent magnet,that does not have a cryostat. In the case of a magnet that does nothave a cryostat, a radio-opaque sleeve (not depicted), constructed, forexample, of a radio-opaque screen stretched over a cage structure orcylinder (such as a tube) formed from non-ferromagnetic materials, canbe inserted into the cavity 116 of the magnet 115 to provide aradio-opaque shield. In an embodiment, the radio-opaque sleeve is openat its service end, and the sleeve combines with service end cap 119 tocomplete the RF shield within the magnet 115. In another embodiment, theradio-opaque sleeve has a closed end, and use of service end cap 119 isoptional.

[0052] In an alternative embodiment that can be used where the NMRmagnet 115 does not have a cryostat 117, an RF shield, for example acopper screen, can be provided on the outside of the magnet 115. In suchan alternative embodiment, the RF shield should be configured so that itsurrounds magnet 115 (except for the opening of magnet cavity 116). Insuch an embodiment, the screen could be connected, and electricalcontact provided, to holder 103 at the patient end of magnet 115.

[0053] In some embodiments, the RF shield for the NMR procedure can beformed without RF shielding provided by the holder. For example, in somecases, the NMR magnet is of sufficient length to permit placement of thepatient into the magnet without the patient or patient support unitextending out of the opening of the magnet. In such cases, aradio-opaque RF screen similar to the service end cap 119, withpenetrations for electrical lines for RF coils and monitoring devices,can be placed over the opening at the patient end of the magnet tocomplete the RF shield for the NMR procedure. Such a radio-opaque screenmay be attached or attachable to the patient support unit as well as tothe magnet. In other embodiments, the radio-opaque bore may be extendedto a length sufficient to achieve the same purpose, for example by useof a radio-opaque cylinder of the same diameter as the bore of themagnet, which may be integral with or attachable to the magnet. In suchan embodiment, the RF shield may be completed by covering the patientend of the radio-opaque cylinder with a radio-opaque RF screen similarto the service end cap 119. In some embodiments, the radio-opaquecylinder can support any portion of the patient support unit thatextends out of the opening of the magnet. In other embodiments, aradio-opaque cylinder may be attached to or an integral part of thepatient support unit. In such embodiments, the radio-opaque cylinder mayhave a radio-opaque base at the patient end, such that when theradio-opaque cylinder is connected to the magnet, a substantiallycomplete RF shield comprising RF shielding provided by the radio-opaquecylinder, and magnet-RF-shielding, is formed. In some embodiments thatdo not rely on the holder to provide RF-shielding, the magnet hasassociated with it, for example as an integral part or as a removableattachment, a ledge for supporting any part of the patient support unitthat extends out of the magnet.

[0054] In the embodiment depicted in FIG. 1A, magnet 115 has associatedwith it a service end cap 119 for providing RF shielding over theopening at the service end 118 of magnet 115. Service end cap 119 may bemade of non-ferromagnetic metal, such as stainless steel, aluminum, orcopper, or metal screen such as copper screen, and may include aperturesfor gradient and imaging cables. Service end cap 119 can be attached tothe service end 118 of magnet 115 by means of hooks, clasps, clamps,clips, screws, bolts, hinges, and other similar means.

[0055] In the embodiment depicted in FIG. 1B, magnet 115 includes RFseals 125, to provide an electrical connection between holder 103 andmagnet 115 to ensure the formation of a continuous RF shield.

[0056] In embodiments of the present invention, magnet 115 also has adocking mechanism (not depicted) for engaging with a docking mechanism(not depicted) on holder 103 to dock holder 103 to magnet 115. Thedocking mechanisms align holder 103 with magnet cavity 116, and track112 with track 121 (depicted in FIG. 1B), and ensure proper placement ofthe holder 103 in relationship to the magnet cavity 116, thusfacilitating easy transfer of the patient support unit 131 into magnetcavity 116.

[0057]FIGS. 2 and 2A depict an embodiment of patient support unit 131,comprising bed 132, bottom section 136, RF coil block 135, lower RFcoils 139 mounted on RF coil block 135, and upper RF coil 137. Bed 132is made of or coated with a material that is suitable for holding ananimal, for example, an easily cleanable, waterproof material that alsoprovides comfort and stability to the animal. Various plastics andnon-conductive materials, including but not limited to fiberglass,Teflon or polyvinyl chloride, are suitable for this application. In theembodiment depicted in FIG. 2A, bed 132 is an integral part of bottomsection 136 of patient support unit 131. In other embodiments, bed 132simply rests on bottom section 136 of patient support unit 131; in stillother embodiments, bed 132 removably attaches to bottom section 136 ofpatient support unit 131.

[0058] Bed 132 is shaped to accommodate an animal. In an embodiment, bed132 is shaped to accommodate the curvature of the animal's spine, inorder to facilitate holding the animal in an inverted position. Thus,bed 132 may have a V-shaped cross section, a U-shaped cross section, orany other cross section that may be suited to hold a particular animal.The V-shaped bed used in the embodiments depicted in FIGS. 2, 2A and 2Baccommodates the spine of many animals, such as many types of cats anddogs, such that the spine of the inverted animal is positionedsubstantially in or near the vertex of the “V”, and therefore in closeproximity to lower RF coils 139—which, as described below, may also haveV-shaped cross-sections—for optimal imaging.

[0059] In the embodiment depicted in FIG. 2, patient support unit 131has associated with it upper RF coils 137 (of which only one isdepicted) and lower RF coils 139. In the embodiment depicted in FIGS. 2and 2A, lower RF coils 139 are mounted on RF coil block 135, whichconforms to the shape of bed 132. In the embodiment depicted in FIG. 2,RF coil block 135 is V-shaped to conform to V-shaped bed 132. In anembodiment, RF coil block 135 is movable in a longitudinal direction,for example along a track (not depicted) formed on the bottom section136 of the patient support unit 131. Thus, for example, when the patientis placed on bed 132, lower RF coils 139 can be moved forward orbackward such that an image of the desired portion of the patient'sspine or abdomen can be obtained. In one embodiment, RF coil block 135can be moved by manipulation of manual controls on the outside of holder103, where the manual controls comprise a pulley and wheel system. Inanother embodiment, RF coil block 135 can be moved back and forth bymeans of a push-pull stick. The movable RF coil arrangement ofembodiments of the invention provides one way for the NMR operator toobtain images of different parts of a patient's body, without moving thepatient.

[0060] In the embodiment depicted in FIG. 2, lower RF coils 139 mayfunction as a plurality of separate coils, or some or all of them may beconnected in series to operate as an array of coils. In someembodiments, lower RF coils 139 comprise parts mounted on each side ofRF coil block 135. For example, in some embodiments, lower RF coils 139are non-planar coils with two loops, such as figure-eight-shaped coils,such that one loop of the coil is mounted on one side of RF coil block135, and the other loop of the coil is mounted on the opposite side ofRF coil block 135. Accordingly, in some embodiments, for a V-shaped bed132 and V-shaped RF coil block 135, the lower RF coils 139 have aV-shaped cross-section, and are thus well-positioned for imaging thespine of an animal in or near the vertex of the “V” of the V-shaped bed.In such a configuration, non-planar lower coils 139 may function aspartial volume coils, because they partially surround the object beingimaged. In some embodiments, lower RF coils 139 comprise parts mountedon only one side of RF coil block 135.

[0061] In embodiments of the present invention, each lower RF coil 139can also be used in combination with a “mate,” such as upper RF coil137, placed above bed 132 to complete a volume coil. In this manner, asdepicted in FIG. 2A, the forward lower RF coil 139 combines with upperRF coil 137 to form a volume coil for imaging the head of the patient.In the same manner, lower RF coils 139 can be combined with upper RFcoils for forming volume coils for imaging a patient's abdomen, asanother example. When used, upper RF coils 137 may be plugged intoconnections (not depicted) in patient support unit 131, to connect themto the appropriate lower RF coils 139. An upper RF coil 137 may comprisea single coil, or an array of coils. The ability to create new RFcoils—such as volume coils—by combining lower RF coils 139 with upper RFcoils 137 enables the NMR operator to obtain images of different partsof a patient's body, without moving the patient.

[0062] Patient support unit 131 can thus accommodate a wide variety ofdifferent RF coil configurations and designs, as will be apparent uponpracticing the invention.

[0063] In the embodiment depicted in FIG. 2, patient bed 132 includes anaperture or apertures (not depicted) to allow for drainage of thepatient's urine or other bodily fluids from the bed into fluidcollection container 143.

[0064] In the embodiment depicted in FIGS. 2A and 2B, RF, physiologicalmonitoring, and other internal electrical or other lines 138 run fromthe interior of patient support unit 131, including from RF coils 137and 139 and from bed 132, to internal electrical panel 133, whichconnects them to external electrical panel 123 on bottom portion 105(depicted in FIGS. 1 and 1B). In the embodiment depicted in FIGS. 1 and1B, external electrical panel 123 is connected, via external lines 134,to magnet electrical panel 122 on magnet 115. Other arrangements forproviding connections to the patient support unit will be apparent uponpracticing the invention.

[0065] In embodiments of the invention, the patient support unit bottomsection 136 is shaped substantially to conform to the bottom portion ofmagnet cavity 116. In the embodiment depicted in FIGS. 1B, 2 and 2A,patient support unit bottom section 136 forms groove 141, which isshaped to receive track 112 of holder bottom portion 105 and track 121of magnet 115, to allow for sliding of the patient support unit alongthe tracks in holder bottom portion 105 and magnet 115. In addition, inthe embodiment depicted in FIG. 1B, in which magnet cavity 116 iscylindrical, patient support unit 131 is curved at least in part with acurvature that substantially matches that of cavity 116.

[0066] In embodiments of the invention, patient support unit bottomsection 136 is constructed of a material that allows for optimal slidingwithin the magnet cavity 116. Good slidability may be achieved whenpatient support unit bottom section 136 is made of or coated withTeflon-coated fiberglass, and the bore of the magnet cavity 116, orcryostat 117, is made of or coated with Teflon-coated carbon fiber.Appropriately coated materials for these purposes can be obtained fromM.T.D. Inc., 24 Slabtown Creek Road, Blairstown, N.J. 07825.

[0067] A patient support unit of this invention, such as patient supportunit 131 of the embodiment depicted in FIGS. 2, 2A, and 2B, can be usedindependently of the RF-shielded holder of the invention describedabove, as, for example, when RF shielding is provided by a faraday cage.

[0068] An embodiment of the invention as depicted in FIGS. 1, 1A, 1B, 1Cand 2A can be used to conduct an NMR procedure as follows, although thesteps need not be performed in the particular sequence, and alternateprocedures will be apparent from use of the invention. A patient,typically anesthetized, is placed in an inverted position in bed 132,which is already in patient support unit 131 (as shown in FIG. 2A),which in turn has been placed in holder bottom portion 105 (as shown inFIG. 1C). Optionally, the patient's limbs may be strapped down by meansof straps (not depicted) to prevent movement. RF coils 137 and 139 arethen positioned appropriately for the NMR procedure to be conducted andthe part of the body to be imaged. If not already in place, holder 103is moved to and docked to magnet 115, in order to facilitate transfer ofthe patient support unit 131 to magnet 115. If not already in place,service end cap 119 is placed on the service end 118 of magnet 115, inorder to complete the portion of the RF shield associated with magnet115. Patient support unit 131 is then moved, typically manually, fromholder bottom portion 105 into cavity 116 of magnet 115, by sliding itfrom track 112 to track 121. Patient support unit 131 may be insertedpartially or fully into the magnet 115, depending on the procedure to beconducted. If patient support unit 131 is partially inserted, thepatient end of patient support unit 131 remains partially on track 112and is supported by holder bottom portion 105. Canopy 109 is placed ontop of holder bottom portion 105 to complete an RF shield around patientsupport unit 131 and the patient. The NMR procedure may then beperformed.

[0069] Conclusion

[0070] While various embodiments of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. For example, the presentinvention is not limited to the physical arrangements or dimensionsillustrated or described; the holder need not be cylindrical in form;and, depending on holder design, a patient end cap may or may not beused. Nor is the present invention limited to any particular design ormaterials of construction. The breadth and scope of the presentinvention should not be limited to any of the above-described exemplaryembodiments, but should be defined in accordance with the followingclaims and their equivalents.

We claim:
 1. A method of providing RF shielding for a patientcomprising: placing the patient on a holder, the holder comprising RFshielding configured for forming a substantially complete RF shieldaround the patient when the holder is adjoined to the cavity of a magnetassociated with magnet-RF-shielding; and adjoining the holder to thecavity of the magnet.
 2. The method of claim 1, further comprisingplacing an RF shield over the service end of the magnet.
 3. The methodof claim 1, wherein the holder comprises a bottom portion comprising RFshielding.
 4. The method of claim 3, wherein the holder furthercomprises a canopy comprising RF shielding.
 5. The method of claim 3,wherein the holder further comprises a patient end cap comprising RFshielding.
 6. The method of claim 4, wherein the canopy removablyattaches to the bottom portion.
 7. The method of claim 5, wherein thepatient end cap removably attaches to the bottom portion or is integralto the bottom portion.
 8. The method of claim 5, wherein the patient endcap comprises apertures.
 9. The method of claim 3, wherein the bottomportion comprises apertures.
 10. The method of claim 1, wherein themagnet-RF-shielding comprises a service end cap.
 11. The method of claim1, wherein the magnet-RF-shielding further comprises a cryostat.
 12. Themethod of claim 11, wherein the magnet-RF-shielding further comprises anRF shield liner configured to combine with the service end cap and theholder-RF-shielding to form a substantially complete RF shield.
 13. Themethod of claim 1, further comprising a positioning means attached tothe holder.
 14. The method of claim 13, wherein the positioning meanscomprises a support configured to support the holder and means forlocomotion.
 15. The method of claim 14, wherein the means for locomotioncomprises wheels.
 16. The method of claim 14, wherein the means forlocomotion comprises rollers.
 17. The method of claim 1, wherein theholder further comprises a patient support unit.
 18. The method of claim1, wherein the patient support unit comprises an RF transmitter antennaand an RF receiver antenna.
 19. The method of claim 17, wherein thepatient support unit comprises an RF coil.
 20. The method of claim 1,where the patient is an animal.
 21. The method of claim 20, wherein thepatient support unit comprises a support configured to hold an animal.22. The method of claim 1, where the patient is human.
 23. The apparatusof claim 22, wherein the patient support unit comprises a supportconfigured to hold a human.
 24. The method of claim 21, wherein thesupport is adapted to hold an animal in an inverted position.
 25. Themethod of claim 24, wherein a cross section of the support is configuredsubstantially to match the curvature of an animal's spine.
 26. Themethod of claim 25, wherein a cross section of the support issubstantially U-shaped.
 27. The method of claim 25, wherein a crosssection of the support is substantially V-shaped.
 28. The method ofclaim 21, wherein the patient support unit comprises straps for holdingan animal.